When using mode 1 or 2, the number returned will NOT match mode 0.
jddayofweek(0, 1) = 'Monday' not 'Sunday' as expected.
This can cause discordance between the UI and the value saved.
jddayofweek
(PHP 4, PHP 5, PHP 7, PHP 8)
jddayofweek — 返回星期几
参数
-
julian_day -
int 类型的儒略日数
-
mode -
历法星期模式 模式 含义 0 (默认) 返回 int 类型的星期几（0 = Sunday， 1 = Monday，等等） 1 以英文返回公历形式的 string 类型的星期几 2 以英文返回公历形式的 string 类型的星期几缩写
返回值
int 或 string 类型的公历星期几。
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User Contributed Notes 2 notes
phimuskapsi at gmail dot com ¶
4 years ago
kevind at communitycolor dot com ¶
7 years ago
You need to check to see how your client wants to represent the day of week. This function returns 0 for Sundays. ISO 8601 uses 7 for Sundays.
BTW, You can also calculate the day of week with modular division:
$dow = (1 + $julianday) % 7; // returns 0 for Sundays.
$dow = ($julianday % 7) + 1; // returns 7 for Sundays.
https://en.wikipedia.org/wiki/Julian_day#Finding_day_of_week_given_Julian_day_number
To make matters confusing. The Julian Date starts at noon UTC. Some programs such as SQLITE3 use real numbers to record date and time. If you pass this function a float; it will return a different day of week for the morning than for the afternoon.
When given a julianday with a decimal part you will need to add a half day and may need further adjustment for your timezone.
